The present invention relates to a driver device which causes a vibrator to produce driving vibrations, a physical quantity measuring device (e.g. vibrating gyroscope) using the driver device, and an electronic instrument.
Gyroscopes are classified as a rotating gyroscope, a vibrating gyroscope, and the like depending on the method of detecting the force applied to an object. In particular, the vibrating gyroscope is considered to be advantageous for reducing size and cost from the viewpoint of the constituent elements and the like.
As a vibrating gyrosensor which detects the angular velocity applied to an object, a piezoelectric vibrating gyrosensor is known which excites a crystal or a piezoelectric element advantageous for increasing reliability and reducing size. The piezoelectric vibrating gyrosensor utilizes a phenomenon in which a Coriolis force occurs perpendicularly to vibrations when an angular velocity is applied to a vibrating object.
For example, the vibrating gyrosensor which detects an angular velocity causes a physical quantity transducer (vibrator) to produce driving vibrations. When an angular velocity is applied to the vibrator, a Coriolis force occurs perpendicularly to driving vibrations to produce detection vibrations. Since the detection vibrations occur perpendicularly to the driving vibrations, the detection signal (signal component due to the detection vibrations) differs in phase from the driving signal (signal component due to the driving vibrations) by 90 degrees. The detection signal can be synchronously detected separately from the driving signal utilizing the above phenomenon, for example.
The vibrating gyrosensor is used in a wide variety of applications, such as shake detection for a video camera or a digital camera, positioning using a global positioning system (GPS) for a car navigation system, and position detection for an aircraft or a robot.
The vibrating gyrosensor used in these applications is driven by a battery. Therefore, it is necessary to increase the life of the battery by reducing the power consumption of the vibrating gyrosensor as much as possible. In this case, it is preferable to stop supplying power to the vibrating gyrosensor when an angular velocity or the like is not detected and to supply power to the vibrating gyrosensor from the battery only when using the vibrating gyrosensor. This makes it necessary to cause the vibrating gyrosensor to perform a normal operation within a short period of time after activation.
Specifically, it is important to cause the vibrating gyrosensor to promptly transition to the operation state in which the gyrosensor can detect the physical quantity (steady oscillation state) when supplying power (during oscillation startup). For example, when using a vibrator such as a crystal vibrator which has a high Q value and requires a long time until stable oscillations are achieved after supplying power, it is considerably difficult to achieve a high-speed transition to the steady oscillation state.
In order to reduce power consumption, it is preferable to suspend the operation of an unnecessary circuit when the physical quantity such as the angular velocity need not be detected. When providing a low power consumption mode (sleep mode), the circuit must be designed to enable a high-speed recovery from the low power consumption mode (sleep mode) to the normal operation mode.
JP-A-2004-286503 and JP-A-2003-240556 disclose technologies for reducing the startup time of the vibrating gyrosensor, for example.
JP-A-2004-286503 discloses technology in which a CR oscillation circuit or a ring vibrator is provided in an oscillation loop so that the oscillation amplitude is increased by an amplifier immediately after activation.
JP-A-2003-240556 discloses technology in which a resistor is provided in series with a crystal vibrator to reduce the period of time until the signal from the vibrator is stabilized.
A driver device for the vibrating gyrosensor must cause the vibrator to constantly vibrate (oscillate) at a resonance frequency in order to stably detect the angular velocity applied to the vibrator. The driver device also must cause the vibrator to oscillate within a short time to start a normal operation. Furthermore, it is preferable to form the driver device using a small circuit with low power consumption in order to increase the life of the battery at low cost.
On the other hand, if the vibrator is formed of a crystal having a high Q value and sealed in a package under vacuum, the Q value of the vibrator increases to a large extent during drive. Therefore, the period of time (startup time) until the signal from the vibrator is stabilized increases when causing the vibrator to produce driving vibrations.
According to the technology disclosed in JP-A-2004-286503, when causing the crystal vibrator to oscillate at a frequency close to the driving frequency of the crystal vibrator, the areas of the capacitor and the resistor of the CR oscillation circuit must be increased. This results in an increase in the size and cost of the vibrating gyroscope (vibrating gyrosensor).
According to the technology disclosed in JP-A-2004-286503, it is difficult to cause a crystal vibrator with a high Q value to operate at its driving frequency because the crystal vibrator is driven at another frequency during the startup. Therefore, the period of time until stable oscillations are achieved increases when affected by a manufacturing variation and the like.
According to the technology disclosed in JP-A-2004-286503, the vibrator is driven by a rectangular wave after oscillations have occurred. Therefore, the energy is lost even in the steady oscillation state, whereby power consumption increases as compared with the case of driving the vibrator by a sine wave.
A low power consumption mode (sleep mode) may be provided as the operation mode of the driver device aiming at reducing its power consumption so that the operation of the circuit is suspended when unnecessary and the normal operation is recovered quickly when necessary. In particular, when causing a crystal vibrator to oscillate, the oscillation startup time increases due to a high Q value. Therefore, it is necessary to at least cause the crystal vibrator to continuously oscillate in order to reduce the normal operation recovery time.
However, according to the technology disclosed in JP-A-2004-286503, when causing the crystal vibrator to oscillate at a frequency close to the driving frequency of the crystal vibrator, the areas of the capacitor and the resistor of the CR oscillation circuit must be increased. This results in an increase in the size and cost of the vibrating gyroscope (vibrating gyrosensor).
According to the technology disclosed in JP-A-2004-286503, it is difficult to cause a crystal vibrator with a high Q value to operate at its driving frequency because the crystal vibrator is driven at another frequency during startup. Therefore, the period of time until stable oscillations are achieved increases when affected by a manufacturing variation and the like. Therefore, the technology disclosed in JP-A-2004-286503 results in an increase in startup time and power consumption, even if a sleep mode is provided.
The technology disclosed in JP-A-2003-240556 requires that a resistor inserted. In general, when incorporating a resistor in an integrated circuit device, it is difficult to apply the desired energy to the vibrator due to a large manufacturing variation of the resistor. According to the technology disclosed in JP-A-2003-240556, the gain is reduced because the energy applied to the vibrator is divided by the resistor.
Therefore, the technology disclosed in JP-A-2003-240556 results in an increase in startup time and power consumption due to the reduced gain, even if a sleep mode is provided.